Nylon staple fiber suitable for use in abrasion resistant, high strength nylon blended yarns and fabrics

ABSTRACT

Included is the preparation of high strength nylon staple fibers having a denier per filament of about 1.0 to 3.0, a tenacity T at break of at least about 6.0, and a load-bearing capacity, T7, of greater than about 2.5, including greater than 3.2. Such nylon staple fibers are produced by preparing tows of relatively high molecular weight nylon filaments (RV of 65 to 100), drawing and annealing such tows via a two-stage drawing and annealing operation and then cutting or otherwise converting the drawn and annealed tows into the desired high strength nylon staple fibers. The nylon staple fibers so prepared can be blended with a companion fiber such as cotton staple fibers to produce nylon/cotton (NYCO) yarns.

FIELD OF THE INVENTION

This invention relates to the preparation of nylon staple fiber suitablefor use in abrasion resistant and acceptably high strength blended yarnsand fabrics such as nylon/cotton (NYCO) yarns and fabrics. Such nylonstaple fiber is produced by preparing tows of relatively high molecularweight quenched nylon filaments, drawing and annealing such tows, andthen cutting or otherwise converting the drawn and annealed tows intothe desired nylon staple fiber.

The nylon staple fiber so prepared can be blended with other fibers suchas cotton staple fiber to produce nylon/cotton NYCO yarns. Such yarnscan then be woven into NYCO fabrics which can be advantageously abrasionresistant, high strength, optionally lightweight, comfortable, lowercost, and durable and hence especially suitable for use in or as, forexample, military apparel such as combat uniforms or other rugged useapparel.

BACKGROUND OF THE RELATED TECHNOLOGY

Nylon has been manufactured and used commercially for a number of years.The first nylon fibers were of nylon 6,6, poly(hexamethylene adipamide),and nylon 6,6 fiber is still made and used commercially as the mainnylon fiber. Large quantities of other nylon fibers, especially nylon 6fiber prepared from caprolactam, are also made and used commercially.Nylon fiber is used in yarns for textile fabrics, and for otherpurposes. For textile fabrics, there are essentially two main yarncategories, namely continuous filament yarns and yarns made from staplefiber, i.e. cut fiber.

Nylon staple fiber has conventionally been made by melt-spinning nylonpolymer into filaments, collecting very large numbers of these filamentsinto a tow, subjecting the tow to a drawing operation and thenconverting the tow to staple fiber, e.g., in a staple cutter. The towusually contains many thousands of filaments and is generally of theorder of several hundred thousand in total denier. The drawing operationinvolves conveying the tow between a set of feed rolls and a set of drawrolls (operating at a higher speed than the feed rolls) to increase theorientation of nylon polymer in the filaments. Drawing is often combinedwith an annealing operation to increase nylon crystallinity in the towfilaments before the tow is converted into staple fiber.

One of the advantages of nylon staple fibers is that they are readilyblended, particularly with natural fibers, such as cotton (oftenreferred to as short staple) and/or with other synthetic fibers, toachieve the advantages derivable from such blending. A particularlydesirable form of nylon staple fiber has been used for many years forblending with cotton, particularly to improve the durability andeconomics of the fabrics made from yarns comprising blends of cottonwith nylon. This is because such nylon staple fiber has a relativelyhigh load-bearing tenacity, as disclosed in Hebeler, U.S. Pat. Nos.3,044,520; 3,188,790; 3,321,448; and 3,459,845, the disclosures of whichare hereby entirely incorporated by reference. As explained by Hebeler,the load-bearing capacity of nylon staple fiber is conveniently measuredas the tenacity at 7% elongation (T₇), and the T₇ parameter has longbeen accepted as a standard measurement and is easily read on an Instronmachine.

The Hebeler process for preparing nylon staple fiber involves the nylonspinning, tow forming, drawing and converting operations hereinbeforedescribed. Improvements in the Hebeler process for preparing nylonstaple fiber have subsequently been made by modifiying the nature of thetow drawing operation and by adding specific types of annealing (or hightemperature treatment) and subsequent cooling steps to the overallprocess. For example, Thompson in U.S. Pat. Nos. 5,093,195, and5,011,645 discloses nylon staple fiber preparation wherein nylon 6,6polymer, having for example a formic acid relative viscosity (RV) of 55,is spun into filaments which are then drawn, annealed, cooled and cutinto staple fiber having a tenacity, T, at break of about 6.8-6.9, adenier per filament of about 2.44, and a load-bearing capacity, T₇, offrom about 2.4 to 3.2. Such nylon staple fibers are further disclosed inthe Thompson patents as being blended with cotton and formed into yarnsof improved yarn strength. (Both of these Thompson patents areincorporated herein by reference in their entirety.)

Nylon staple fibers prepared in accordance with the Thompson technologyhave been blended into NYCO yarns (generally at a 50:50 nylon/cottonratio) with these yarns being used to prepare NYCO fabrics. Such NYCOfabrics, e.g., woven fabrics, find application in military combatuniforms and apparel. While such fabrics have generally provensatisfactory for military or other rugged apparel use, militaryauthorities, for example, are continually looking for improved fabricswhich may be abrasion resistant, high strength, lighter in weight, lowerin cost and/or more comfortable but still highly durable or even ofimproved durability.

One route to such fabrics of improved abrasion resistance, durabilityand comfort and optionally lighter weight could involve preparation ofNYCO yarns, and fabrics made therefrom, wherein the nylon staple fibersused in yarn preparation have suitably high load-bearing capacity andcan also impart abrasion resistance properties to yarns and fabrics madetherefrom. Fabrics prepared from yarns using such nylon staple fiberscould advantageously be made to have improved abrasion resistance anddurability in comparison with currently used fabrics. Such nylon staplefibers could also provide such desirable abrasion resistance anddurability performance by being incorporated into lighter weight and/orlower cost fabric which potentially uses less of the nylon staple fiberthan is currently employed in such fabrics.

SUMMARY OF THE INVENTION

Given the foregoing considerations, some embodiments are directed to aprocess for preparing nylon staple fibers which can be blended with acompanion fiber to form a yarn and woven into fabrics to improve fabricstrength and abrasion resistance. Also included are processes forpreparing the staple fibers themselves, and to yarns made by blendingthese nylon staple fibers with a companion fiber such as cotton staplefibers. The resulting blended yarns can then be woven into abrasionresistant, durable and optionally lightweight woven fabrics which areespecially suitable for military or other rugged apparel use.

In process aspects of some embodiments are a process for preparing nylonstaple fibers. This process comprises the steps of melt-spinning nylonpolymer into filaments, quenching the filaments and forming a tow from amultiplicity of these quenched filaments, subjecting the tow to drawingand annealing, and then converting the resulting drawn and annealed towinto staple fibers suitable for forming into, for example, spun yarn.

In accordance with the process aspects of some embodiments, the nylonpolymer which is melt spun into filaments will have a formic acidrelative viscosity (RV) of from 65 to 100. Further, the drawing andannealing of the tow is carried out in a two-stage continuous operationconducted at a total effective draw ratio of from 2.3 to 4.0, includingfrom 3.0 to 4.0. In a first drawing stage of this drawing operation,from 85% to 97.5% of the drawing of the tow occurs. In a secondannealing and drawing stage of this operation, the tow is subjected toan annealing temperature of from 145° C. to about 205° C. In oneembodiment, the temperature of the tow in this annealing and drawingstage may be achieved by contacting the tow with a steam-heated metalplate that is positioned between the first stage draw and the secondstage drawing and annealing operation. This drawing and annealingoperation is then followed by a cooling step wherein the drawn andannealed tow is cooled to a temperature of less than 80° C. Throughoutthe two stage drawing and annealing operation, the tow is maintainedunder a controlled tension.

Another aspectis directed to nylon staple fibers of the type which canbe prepared in accordance with the foregoing process. Thus, the nylonstaple fibers of this invention are those which have a denier perfilament of from about 1.0 to 3.0, a tenacity of at least about 6.0grams per denier and a load-bearing capacity of greater than 2.5, suchas greater than 3.2, grams per denier, measured as tenacity (T₇) at 7%elongation. These staple fibers are fashioned from nylon polymer havinga relative viscosity of from 65 to 100.

In another aspect, the present invention is directed, to textile yarnwhich can be made by blending the nylon staple fibers herein with cottonstaple fibers. The resulting nylon/cotton, i.e., NYCO, yarn thuscomprises both cotton staple fibers and nylon staple fibers in a weightratio of cotton to nylon fibers which ranges from 20:80 to 80:20.Substantially all of the nylon staple fibers in the NYCO yarn are thosewhich comprise nylon polymer having a formic acid RV of from 65 to 100,which have a denier per filament of from 1.0 to 3.0, a tenacity of atleast 6.0 grams per denier and a load bearing capacity of greater than2.5, and more preferably greater than 3.2 grams per denier, measured astenacity (T₇) at 7% elongation.

In another aspect, the present invention is directed to lightweight anddesirably durable NYCO fabrics which are woven from the NYCO textileyarns hereinbefore described. Such fabrics are woven from textile yarnsin both a warp and a weft (fill) direction. The yarns woven in at leastone of these directions will be a yarn comprising blended nylon staplefibers herein and cotton staple fibers in a cotton fiber to nylon fiberweight ratio of from about 20:80 to 80:20. Again, substantially all ofthe nylon staple fibers in the textile yarns used to weave the NYCOfabrics herein are those which comprise nylon polymer having a formicacid RV of from 65 to 100, which have a denier per filament of fromabout 10.0 to 3.0, a tenacity of at least about 6.0 grams per denier anda load-bearing capacity of greater than about 2.5 grams per denier, suchas greater than 3.2 grams per denier, measured as tenacity (T₇) at 7%elongation. In another embodiment the nylon staple fibers may be thosewhich comprise a tenacity of at least about 6.0 grams per denier and aload bearing capacity, measured as (T₇) greater than about 3.2 grams perdenier.

In still another aspect are fabrics including a blended yarn such asNYCO fabrics woven from textile yarns in both a warp and weft (fill)direction wherein these textile yarns woven in both directions compriseblended cotton staple fibers and nylon staple fibers in a weight ratioof cotton staple fibers to nylon staple fibers ranging from 20:80 to80:20. Further, in such fabrics the NYCO yarns woven in the weft (fill)direction comprise nylon staple fibers having a denier per filament offrom 1.3 to 2.0, including from 1.55 to 1.8, 1.6 to 1.8 and from 1.55 to1.75, and the NYCO yarns woven in the warp direction comprise nylonstaple fibers having a denier per filament of from 2.1 to 3.0, includingfrom 2.3 to 2.7. In yet another embodiment, the yarns used in the warpand weft directions, respectively, may be differentiated by otherphysical properties or performance specifications. For example, a fabricmay be constructed with yarns in the warp direction that have relativelyhigher abrasion resistance, but lower tensile strength, as compared toyarns used in the weft direction.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the terms “durable” and “durability” refer to thepropensity of a fabric so characterized to have suitably high grab andtear strength as well as resistance to abrasion for the intended end useof such fabric, and to retain such desirable properties for anappropriate length of time after fabric use has begun.

As used herein, the term blend or blended, in referring to a spun yarn,means a mixture of fibers of at least two types, wherein the mixture isformed in such a way that the individual fibers of each type of fiberare substantially completely intermixed with individual fibers of theother types to provide a substantially homogeneous mixture of fibers,having sufficient entanglement to maintain its integrity in furtherprocessing and use.

As used herein, cotton count refers to the yarn numbering system basedon a length of 840 yards, and wherein the count of the yarn is equal tothe number of 840-yard skeins required to weigh 1 pound.

All numerical values recited herein are understood to be modified by theterm “about”.

Some embodiments are based on the preparation of improved nylon staplefibers having certain specified characteristics and on the subsequentpreparation of yarns, and fabrics woven from such yarns, wherein theseimproved nylon staple fibers are blended with at least one other fiber,also referred to as a companion fiber. The other fibers may includecelluosics such as cotton, modified cellulosics such as FR treatedcelluose, polyester, rayon, animal fibers such as wool, fire resistant(FR) polyester, FR nylon, FR rayon, FR treated cellulose, m-aramid,p-aramid, modacrylic, novoloid, melamine, polyvinyl chloride, antistaticfiber, PBO (1,4-benzenedicarboxylic acid, polymer with4,6-diamino-1,3-benzenediol dihydrochloride), PBI (polybenzimidazole),and combinations thereof. The nylon staple fibers of some embodimentscan provide an increase in strength and/or abrasion resistance to yarnsand fabrics. This is especially true for combination with relativelyweaker fibers such as cotton and wool.

The specific characteristics of the nylon staple fibers prepared andused herein include formic acid RV of the nylon used to make the fiber,fiber denier, fiber tenacity and fiber load-bearing capacity defined interms of fiber tenacity at 7% elongation.

Realization of the desired nylon staple fiber material herein is alsobased on the use in staple fiber manufacture of nylon polymeric materialhaving certain selected properties. The nylon polymer itself which isused for the spinning of nylon filaments can be produced in conventionalmanner. Nylon polymer suitable for use in the process and filaments ofthis invention consists of synthetic melt spinnable or melt spunpolymer. Such nylon polymers can include polyamide homopolymers,copolymers, and mixtures thereof which are predominantly aliphatic,i.e., less than 85% of the amide-linkages of the polymer are attached totwo aromatic rings. Widely-used polyamide polymers such aspoly(hexamethylene adipamide) which is nylon 6,6 and poly(E-caproamide)which is nylon 6 and their copolymers and mixtures can be used inaccordance with some embodiments. Other polyamide polymers which may beadvantageously used are nylon 12, nylon 4,6, nylon 6,10, nylon 6,12,nylon 12,12, and their copolymers and mixtures. Illustrative ofpolyamides and copolyamides which can be employed in the process,fibers, yarns and fabrics of this invention are those described in U.S.Pat. Nos. 5,077,124, 5,106,946, and 5,139,729 (each to Cofer et al.) andthe polyamide polymer mixtures disclosed by Gutmann in Chemical FibersInternational, pages 418-420, Volume 46, December 1996. Thesepublications are all incorporated herein by reference.

Nylon polymer used in the preparation of nylon staple fibers hasconventionally been prepared by reacting appropriate monomers,catalysts, antioxidants and other additives, such as plasticizers,delustrants, pigments, dyes, light stabilizers, heat stabilizers,antistatic agents for reducing static, additives for modifying dyeability, agents for modifying surface tension, etc. Polymerization hastypically been carried out in a continuous polymerizer or batchautoclave. The molten polymer produced thereby has then typically beenintroduced to a spin pack wherein it is forced through a suitablespinneret to form filaments which are quenched and then formed into towsfor ultimate processing into nylon staple fiber. As used herein, spinpack is comprised of a pack lid at the top of the pack, a spinneretplate at the bottom of the pack and a polymer filter holder sandwichedbetween the former two components. The filter holder has a centralrecess therein. The lid and the recess in the filter holder cooperate todefine an enclosed pocket in which a polymer filter medium, such assand, is received. There are provided channels interior to the pack toallow the flow of molten polymer, supplied by a pump or extruder totravel through the pack and ultimately through the spinneret plate. Thespinneret plate has an array of small, precision bores extendingtherethrough which convey the polymer to the lower surface of the pack.The mouths of the bores form an array of orifices on the lower surfaceof the spinneret plate, which surface defines the top of the quenchzone. The polymer exiting these orifices, is in the form of filamentswhich are then directed downwards through the quench zone.

The extent of polymerization carried out in the continuous polymerizeror batch autoclave can generally be quantified by means of a parameterknown as relative viscosity or RV. RV is the ratio of the viscosity of asolution of nylon polymer in a formic acid solvent to the viscosity ofthe formic acid solvent itself. Determination of RV is described ingreater detail in the Test Methods section hereinafter. RV is taken asan indirect indication of nylon polymer molecular weight. For purposesherein, increasing nylon polymer RV is considered synonymous withincreasing nylon polymer molecular weight.

As nylon molecular weight increases, its processing becomes moredifficult due to the increasing viscosity of the nylon polymer.Accordingly, continuous polymerizers or batch autoclaves are typicallyoperated to provide nylon polymer for eventual processing into staplefiber wherein the nylon polymer has an RV value of about 60 or less.

It is known that for some purposes, provision of nylon polymer ofgreater molecular weight, i.e., nylon polymer having RV values ofgreater than 70-75 and up to 140 or even 190 and higher can beadvantageous. It is known, for example, that high RV nylon polymer ofthis type has improved resistance to flex abrasion and chemicaldegradation. Accordingly, such high RV nylon polymer is especiallysuitable for spinning into nylon staple fiber which can advantageouslybe used for the preparation of papermaking felts. Procedures andapparatus for making high RV nylon polymer and staple fiber thereformare disclosed in U.S. Pat. No. 5,236,652 to Kidder and in U.S. Pat. Nos.6,235,390; 6,605,694; 6,627,129 and 6,814,939 to Schwinn and West. Allof these patents are incorporated herein by reference in their entirety.

In accordance with the present invention, it has been discovered thatstaple fibers prepared from nylon polymer having an RV value higher thanthat generally obtained via polymerization in a continuous polymerizeror batch autclave, and processed in accordance with the spinning,quenching, drawing and annealing procedures described herein, canexhibit suitably high load-bearing capacity as quantified by their T₇tenacity at 7% elongation values, even at lower draw ratios. When suchrelatively high RV nylon staple fibers of suitably high load-bearingcapacity are blended with cotton staple fibers, textile yarns ofsuitably high strength can be realized. NYCO fabrics woven from suchyarns exhibit the advantages hereinbefore described with respect toabrasion resistance, strength, durability, optionally lighter weight,comfort and/or lower cost.

In accordance with the staple fiber preparation process herein, nylonpolymer which is melt spun into tow-forming filaments through one ormore spin pack spinnerets and quenched will have an RV value rangingfrom about 65 to 100. In one embodiment, the RV of the nylon polymermelt spun into tow-forming filaments herein will have an RV of fromabout 68 to 95 or even 70 to 85. Nylon polymer of such RVcharacteristics can be prepared, for example, using the melt blending ofpolyamide concentrate procedure of the aforementioned Kidder '652patent. Kidder discloses certain embodiments in which the additiveincorporated into the polyamide concentrate is a catalyst for thepurpose of increasing the formic acid relative viscosity (RV). Higher RVnylon polymer available for melting and spinning can also be provided bymeans of a solid phase polymerization (SPP) step wherein nylon polymerflakes or granules are conditioned to increase RV to the desired extent.Such solid phase polymerization (SPP) procedures are described ingreater detail in the aforementioned Schwinn/West '390, '694, '129 and'939 patents.

The nylon polymer material prepared as hereinbefore described and havingthe requisite RV characteristics as specified herein are fed to a spinpack, for example via a twin screw melter device. In the spin pack thenylon polymer is spun by extrusion through one or more spinnerets into amultiplicity of filaments. For purposes herein, the term “filament” isdefined as a relatively flexible, macroscopically homogeneous bodyhaving a high ratio of length to width across its cross-sectional areaperpendicular to its length. The filament cross section can be anyshape, but is typically circular. Herein, the term “fiber” can also beused interchangeably with the term “filament”.

Each individual spinneret position may contain from 100 to 1950filaments in an area as small as 9 inches by 7 inches (22.9 cm×17.8 cm).Spin pack machines may contain from one to 96 positions, each of whichprovides bundles of filaments which eventually get combined into asingle tow band for drawing/downstream processing with other tow bands.

After exiting the spinneret(s) of the spin pack, the molten filamentswhich have been extruded through each spinneret are typically passedthrough a quench zone wherein a variety of quenching conditions andconfigurations can be used to solidify the molten polymer filaments andrender them suitable for collection together into tows. Quenching ismost commonly carried out by passing a cooling gas, e.g., air, toward,onto, with, around and through the bundles of filaments being extrudedinto the quenching zone from each spinneret position within the spinpack.

One suitable quenching configuration is cross-flow quenching wherein thecooling gas such as air is forced into the quenching zone in a directionwhich is substantially perpendicular to the direction that the extrudedfilaments are travelling through the quench zone. Cross-flow quenchingarrangements are described, among other quenching configurations, inU.S. Pat. Nos. 3,022,539; 3,070,839; 3,336,634; 5,824,248; 6,090,485,6,881,047 and 6,926,854, all of which patents are incorporated herein byreference.

An important aspect of the staple fiber preparation process herein isthat the extruded nylon filaments used to eventually form the desirednylon staple fibers should be spun, quenched and formed into tows withboth positional uniformity and uniformity of quenching conditions whichare sufficient to permit use of draw ratios that provide the desiredeventual staple fiber T₇ tenacity, e.g., a T₇ greater than 2.5 grams perdenier or, in another embodiment, greater than 3.2 grams per denier.Positional uniformity includes both within-position uniformity andposition-to-position uniformity.

Both types of positional uniformity can be improved by carefullycontrolling temperature of the nylon polymer fed to the spin pack, asopposed to simply monitoring temperature of the heat exchange mediumused to heat the polymer supply lines and pack wells. U.S. Pat. No.5,866,050, incorporated herein by reference, discloses a method tobetter control nylon polymer temperature and refers to the importance ofhaving a uniform polymer temperature. The specific method disclosed inorder to achieve this result involves a first temperature controlarrangement for heating the spin pack to a first predetermined referencetemperature greater than the predetermined polymer inlet temperaturesuch that the temperature across a polymer filter holder and thespinneret plate in the spin pack is substantially uniform. A plateassembly having at least one polymer flow passage therein is disposedbetween the outlet of the pump and the inlet of the spin pack. A secondtemperature control arrangement for independently controlling thetemperature of the plate assembly to a second predetermined referencetemperature is provided. The temperature control strategy and methodsused in accordance with the invention disclosed herein is quitedifferent as will be subsequently described.

Remelting of the polymer, e.g., in a twin screw melter, rather thanfeeding polymer from a continuous polymerization (CP) operation, canalso help provide polymer to the spin pack and quench chimney(s) at auniform controlled temperature. A twin screw melter has the ability tomeasure and control polymer temperature at various locations prior todelivery to the spinneret versus a continuous polymerization unit whichonly measures heat exchange medium temperature at similar locationsprior to the spinneret/pack. In connection with development of theprocesses disclosed herein, it was observed that the variation ofpolymer temperature in the in the transit line between the polymerizerand the spin pack when run in continuous operation for an extendedperiod of time was reduced from +/−2.5 C to +/−0.6 C when a continuouspolymerizer operation was replaced by a twin screw melter. Polymer madefrom a continuous polymerizer also is known to contain gel which isdegraded or cross-linked polymer. Gel can cause downstream drawingissues in terms of broken filaments. It is well known that use of a twinscrew melter has been found to reduce the amount of gel versus a polymersupply from a CP unit. This is an example of features of the polymersupply which enable the extruded filaments to be made more uniformilyand draw at higher ratios.

Spin center position-to-position filament bundle uniformity can alsoaffect downstream draw processing. Sources of position-to-positionfilament bundle uniformity problems start with the machine and quenchmedium design. Use of fewer spin positions can facilitate improvementsin position-to-position uniformity. Spin machines having 20 or fewerspinneret positions are easier to control with respect to maintenance ofconstant quench medium pressure along the length of the spin machineduct work, versus for example, 40 or even 96 positions. Fewer positionscoupled with having the quench medium duct work reduced in length byapproximately 50% from conventional practice allows for provision of amore uniform, non-turbulent quench medium supply to the spin center.

Another design feature of the spin center which facilitates uniformfilament production relates to the quench medium filtering system. Animproved quench air filter system, upstream of the spin center,continually monitors pressure drop across the filters to control postfilter air flow and pressure. Air flow and pressure is a function of theproduct spun. Other design features of the spin center which can provideimproved position-to-position filament unfomity is to have thepack/spinneret positioned exactly in the center of the quench chimney.All of these design features improve the position-to-position uniformityof the product being spun on the machine and contribute to improvementsin the downstream drawing performance of tows formed from the filamentswhich are spun and quenched.

Within-position filament uniformity has the largest effect ondownstreaming processing of tows and on obtaining the desired resultingstaple fiber properties. Numerous prior art references discuss theproblems encountered in obtaining filaments with uniform properties madeat higher throughputs and using high filament density melt spinningprocesses. U.S. Pat. No. 4,248,581 mentions the quenching of filamentsin a uniform manner and the difficulties associated with cross-flowquench. These same issues are also discussed in the '539, '839, '634,'248; '485, '047 and '854 patents hereinbefore referenced. Overcomingsuch within-position problems associated with uniformity of quenchingconditions within the quenching zone is an important factor inpermitting utilization of generally higher draw ratios which arepreferred for use in the subsequent drawing/annealing stage of theprocess herein.

In some cross-flow quenching operations, quench air is forced throughthe molten polymer filament bundles from one side of a rectangularfilament array. Issues which can arise from this type of filamentquenching are that the rows of filaments closest to the air flow quenchfirst or quicker while the rows of filaments further from the air flowquench at a later time. It has also been shown in numerous patents thatthe quench air gets pulled with the filaments' downward movement andheated as it moves through the filament array or bundle. Thiscontributes to uneven quenching of the molten filaments. Such uneven,nonuniform quench can cause crystallization differences between thefront, middle and back filaments. If this crystallization difference islarge enough, it can cause fibers in the filament bundles to draw moreor less. In other words, those filaments fully quenched early in thequench chimney versus later may not draw to the same ratio. This, inturn, can lead to excessive filament breaks when the tows formed fromsuch non-uniform filaments are drawn at higher draw ratios or can limitthe draw ratio that can be used due to inoperability of the drawmachine.

As noted in the publication Ziabicki; “Fundamentals of Fibre Formation”,(J Wiley &Sons), 1976, p 196 ff and p 241, the cooling conditionsdirectly below the nozzle package are decisive for the thread quality.In addition, the bundle of threads exerts a considerable resistance tothe quench medium flow, which may stem from the fact that the blow airflows around the bundle instead of flowing through the same. Ziabickialso discloses that even more dramatic effects are observed intemperature distribution. The differences in air temperature measuredbefore and beyond the bundle as well inside the bundle, can besubstantial. He cites another study in which the structure andmechanical properties of filaments taken from various parts of thebundle were related to the range of air temperature in the individualparts of the bundle. Ziabicki concludes that the consequence ofnon-uniform structure is, as a rule, variation of yield stress andstress-strain characteristics. The consequence of this effect is that ifmaterial subjected to drawing consists of differing structure, theeffective draw ratio in various sections will also be different.

Turbulent quench medium flow such as eddy currents can cause moltenfilaments to come in contact with one another and stick. These stuckfibers can also lead to downstream filament breakage problems.

To minimize problems of the foregoing types, the quenching zone orchamber used in the process of the present invention should be designedand configured such that all of the filament bundles are exposed tosubstantially the same quenching conditions during the same time frame.An important factor in creating such uniform quenching conditions withinthe quenching zone relates to provision of controlled and uniform flowof the cooling gas, e.g., air, during its introduction into, flowthrough, and exit from the quenching zone or chamber.

A number of features can be used to improve the uniformity of quench airflow. Baffles can be positioned in the chimney to prevent air flowingaround the bundle versus through the bundle. These baffles can beadjusted to also prevent eddy currents or turbulent air in the chimneythat would normally result in stuck, molten filaments. Perforations inthe chimney doors or tubes can also be used to better control turbulenceof the quench medium. U.S. Pat. Nos. 3,108,322; 3,936,253 and 4,045,534,incorporated herein by reference, disclose the use of baffles andperforations in chimney quench systems to improve quench and reducestuck filaments.

Another modification that can be used to improve positional uniformityis use of a monomer collection device that allows for positionaladjustment as well as adjustment in terms of overall vacuum pulledacross the machine. A suitable monomer collection device can also have alarger rectangular opening that can be used to pull additional air ifneeded though the bundle but controlled to prevent filaments fromleaving the bundle.

Overall by using a combination of some or all of the foregoing spinningand quenching features to ensure spun supply uniformity, i.e., moreuniform undrawn fibers in terms of denier per filament, crystallinity,etc., such fibers can accordingly be drawn more during thedrawing/annealing step hereinafter described without an undue incidenceof filament breaks. This in turn permits preparation of nylon staplefibers of higher tenacity at 7% elongation and at break.

The quenched spun filaments which have been formed using the foregoinguniformity-enhancing techniques can be combined into one or more tows.Such tows formed from filaments from one or more spinnerets are thensubjected to a two stage continuous operation wherein the tows are drawnand annealed.

Drawing of the tows is generally carried out primarily in an initial orfirst drawing stage or zone wherein bands of tows are passed between aset of feed rolls and a set of draw rolls (operating at a higher speed)to increase the crystalline orientation of the filaments in the tow. Theextent to which tows are drawn can be quantified by specifying a drawratio which is the ratio of the higher peripheral speed of the drawrolls to the lower peripheral speed of the feed rolls.

The first drawing stage or zone may include several sets of feed anddraw rolls as well as other tow guiding and tensioning rolls such assnubbing pins. Draw roll surfaces may be made of metal, e.g., chrome, orceramic.

Ceramic draw roll surfaces have been found to be particularlyadvantageous in permitting use of the relatively higher draw ratiosspecified for use in connection with the staple fiber preparationprocess herein. Ceramic rolls improve roll life as well as provide asurface that is less prone to wrap. An article appearing theInternational Fiber Journal (International Fiber Journal, 17,1, February2002: “Textile and Bearing Technology for Separator Rolls, Zeitz andel.) as well as U.S. Pat. No. 4,494,608, both incorporated herein byreference, also disclose the use of ceramic rolls in to improve rolllife and reduce fiber adherence to roll surface.

Particular arrangements of apparatus elements for effecting drawing ofthe tows are described in the hereinbefore mentioned Hebeler U.S. Pat.Nos. 3,044,520; 3,188,790; 3,321,448; and 3,459,845, and in ThompsonU.S. Pat. Nos. 5,093,195 and 5,011,645, all of which patents areincorporated herein by reference. The preferred ceramic rolls can, forexample, be installed as some or all of the rolls labelled as Elements12, 13 and 22 in FIG. 2 of the Thompson U.S. Pat. No. 5,093,195.

While the greatest extent of drawing of the tows of filaments hereintakes place in the initial or first drawing stage or zone, someadditional drawing of the tows will generally also take place in asecond or annealing and drawing stage or zone hereinafter described. Thetotal amount of draw to which the filament tows herein are subjected canbe quantified by specifying a total effective draw ratio which takesinto account drawing that occurs in both a first initial drawing stageor zone and in a second annealing and drawing stage or zone.

In the process of this invention, the tows of nylon filaments aresubjected to a total effective draw ratio of from 2.3 to 4.0, oralternatively from 3.0 to 4.0. In one embodiment wherein the denier perfilament of the tows is generally smaller, a total effective draw ratiocan range from 2.5 to 3.40, from 2.5 to 3.0, and from 3.12 to 3.40. Inanother embodiment, wherein the denier per filament of the tows isgenerally larger, the total effective draw ratio can range from 3.25 to4.0, such as from 3.5 to 4.0, and from 3.25 to 3.75.

In the process of some embodiments, most of the drawing of the tows, asnoted hereinbefore, occurs in the first or initial drawing stage orzone. In particular, from 85% to 97.5%, or more preferably from 92% to97%, of the total amount of draw imparted to the tows will take place inthe first or initial drawing stage or zone. The drawing operation in thefirst or initial stage will generally be carried out at whatevertemperature the filaments have when passed from the quench zone of themelt spinning operation. Frequently, this first stage drawingtemperature will range from 80° C. to 125° C.

From the first or initial drawing stage or zone, the partially drawntows are passed to a second annealing and drawing stage or zone whereinthe tows are simultaneously heated and further drawn. Heating of thetows to effect annealing serves to increase crystallinity of the nylonpolymer of the filaments. In this second annealing and drawing stage orzone, the filaments of the tows are subjected to an annealingtemperature of from 145° C. to 205° C. More preferably, an annealingtemperature of from 165° C. to 205° C. is used. In one embodiment, thetemperature of the tow in this annealing and drawing stage may beachieved by contacting the tow with a steam-heated metal plate that ispositioned between the first stage draw and the second stage drawing andannealing operation.

After the annealing and drawing stage of the process herein, the drawnand annealed tows are cooled to a temperature of less than 80° C., morepreferably less than 75° C. Throughout the drawing, annealing andcooling operations described herein, the tows are maintained undercontrolled tension and accordingly are not permitted to relax.

After drawing, annealing and cooling, the multifilament tows areconverted into staple fiber in conventional manner, for example using astaple cutter. Staple fiber formed from the tows will frequently rangein length from 2 to 13 cm (0.79 to 5.12 inches). More preferably, staplefibers of from 2 to 12 cm (0.79 to 4.72 inches) or from 2 to 12.7 cm(0.79 to 5.0 inches) or even from 5 to 10 cm can be formed. The staplefiber herein can be crimped, but more preferably will not be crimped.

The nylon staple fibers formed in accordance with some embodiments willgenerally be provided as a collection of fibers, e.g., as bales offibers, having an denier per fiber of 1.0 to 3.0. When staple fibershaving a denier per fiber of from 1.6 to 1.8 are to be prepared, a totaleffective draw ratio of from 2.5 to 3.0 can be used in the processherein to provide staple fibers of the requisite load-bearing capacity.When fibers having a denier per fiber of from 2.1 to 3.0, or from 2.5 to3.0, are to be prepared, a total effective draw ratio of from about,3.25 to 3.75 should be used in the process herein to provide staplefibers of the requisite load-bearing capacity.

The nylon staple fibers herein will have a load-bearing capacity ofgreater than 2.5 grams per denier such as greater than 3.2 grams perdenier, measured as tenacity (T₇) at 7% elongation. The T₇ values of thenylon staple fibers herein will range from 2.5 to 5.0 grams per denier,including from 3.0 to 5.0, fromfrom 3.3 to 4.0 grams per denier, andfrom 3.4 to 3.7 grams per denier. The nylon staple fibers herein mayalso have a tenacity T at break of at least about 6.0 grams per denier.Tenacity T at break of the staple fibers of some embodiments may begreater than 6.5 grams per denier, including the range from 7.0 to 8.0grams per denier.

The nylon staple fibers provided herein are especially useful forblending with other fibers for various types of textile applications.Blends can be made, for example, with the nylon staple fibers of someembodiments in combination with other synthetic fibers such as rayon orpolyester. Blends of the nylon staple fibers herein can also be madewith natural cellulosic fibers such as cotton, flax, hemp, jute and/orramie. Suitable methods for intimately blending these fibers mayinclude: bulk, mechanical blending of the staple fibers prior tocarding; bulk mechanical blending of the staple fibers prior to andduring carding; or at least two passes of draw frame blending of thestaple fibers subsequent to carding and prior to yarn spinning.

In accordance with one embodiment, the high load-bearing capacity nylonstaple fibers herein may be blended with cotton staple fibers and spuninto textile yarn. Such yarns may be spun in conventional manner usingcommonly known short and long staple spinning methods including ringspinning, air jet or vortex spinning, open end spinning, or frictionspinning. The resulting textile yarn will generally have a cotton fiberto nylon fiber weight ratio of from 20:80 to 80:20, more preferably from40:60 to 60:40, and frequently a cotton:nylon weight ratio of 50:50. Itis well-known in the art that nominal variation of the fiber content,e.g., 52:48 is also considered to be a 50:50 blend. Textile yarns madewith the high load-bearing capacity nylon staple fibers herein willfrequently exhibit LEA product values of at least 2800, more includingat least 3000 at 50:50 NYCO content. Alternatively, such yarns may havea breaking tenacity of at least 17.5 or 18 cN/tex, including at least 19cN/tex, at 50:50 NYCO content.

In one embodiment, textile yarns herein will be made from nylon staplefibers having a denier per filament of from 1.6 to 1.8 or alternativelyfrom 1.55 to 1.75. In another embodiment, the textile yarns herein willbe made from nylon staple fibers having a denier per filament of from2.1 to 3.0, such as from 2.5 to 3.0, or from 2.3 to 2.7.

The nylon/cotton (NYCO) yarns of some embodiments can be used inconventional manner to prepare NYCO woven fabrics of especiallydesirable properties for use in military or other rugged use apparel.Thus such yarns may be woven into 2×1 or 3×1 twill NYCO fabrics. SpunNYCO yarns and 3×1 twill woven fabrics comprising such yarns are ingeneral described and exemplified in U.S. Pat. No. 4,920,000 to Green.This '000 patent is incorporated herein by reference.

NYCO woven fabrics, of course, comprise both warp and weft (fill) yarns.The woven fabrics of the present invention are those which have the NYCOtextile yarns herein woven in an least one, and preferably both, ofthese directions. In one particularly preferred embodiment, fabricsherein of especially desirable durability and comfort will have yarnswoven in the weft (fill) direction comprising nylon staple fibers hereinwhich have a denier per filament of from 1.6 to 1.8 or from 1.55 to 1.75and will have yarns woven in the warp direction comprising nylon staplefibers herein which have a denier per filament of from 2.1 to 3.0 orfrom 2.5 to 3.0 denier per filament.

The woven fabrics herein made using yarns which comprise the abrasionresistant and/or high load bearing nylon staple fibers herein can useless of the nylon staple fibers than conventional NYCO fabrics whileretaining many of the desirable properties of such conventional NYCOfabrics. Thus, such fabrics can be made to be relatively lightweight andlow cost while still desirably abrasion resisitant, high strength and/ordurable. Alternatively, such fabrics can be made using equal or evengreater amounts of the nylon staple fibers herein in comparison withnylon fiber content of conventional NYCO fabrics with such fabricsherein providing superior durability properties.

Lightweight fabrics of the some embodiments, such are NYCO fabrics mayhave a fabric weight of less than 220 grams/m² (6.5 oz/yd²), includingless than 200 grams/m² (6.0 oz/yd²), or less than 175 grams grams/m²(5.25 oz/yd²). Durable NYCO fabrics of some embodiments such ase NYCOfabrics may have a grab strength of 190 lbs or greater in the warpdirection and 80 lbs or greater in the weft (fill) direction. Otherdurable fabrics herein will be those having a Tear Strength in “asreceived” fabric in warp direction of 11.0 lbf (pound·foot) or greaterand fill direction of 9.0 lbf or greater.

Other durable fabrics herein will be those having a Taber AbrasionResistance of at least 600 cycles to failure, more preferably atleast-1000 cycles to failure. Other durable fabrics herein will have aflex abrasion of 50,000 (cycles) or greater in warp and fill directions.Preferred fabric blend ratio is nominal 50/50, such as 50/50 nyloncotton. It will be recognized by one skilled in the art that abrasionresistance performance will be dependent upon the fabric weight, withhigher fabric weights favoring improved performance. When prepared inthe fabric weight range of 5.6-6.5 oz/yd², the fabrics disclosed hereinexhibit Flex Abrasion values that range from 60,000 cycles to as high as70,000 cycles in the warp direction and 68,000 to 80,000 in the filldirection. Values are to be compared in the “as received” condition.Taber abrasion values for the same above mentioned fabric constructionscan range from 600 cycles to 1900 cycles in the “as received” orunlaundered state.

Test Methods

When the various parameters, properties and characteristics for thepolymers, fibers, yarns and fabrics herein are specified, it isunderstood that such parameters, properties and characteristics can bedetermined using the following types of testing procedures andequipment:

Nylon Polymer Relative Viscosity

The formic acid RV of nylon materials used herein refers to the ratio ofsolution and solvent viscosities measured in a capillary viscometer at25° C. The solvent is formic acid containing 10% by weight of water. Thesolution is 8.4% by weight nylon polymer dissolved in the solvent. Thistest is based on ASTM Standard Test Method D 789. Preferably, the formicacid RVs are determined on spun filaments, prior to or after drawing,and can be referred to as spun fiber formic acid RVs.

Instron Measurements on Staple Fibers

All Instron measurements of staple fibers herein are made on singlestaple fibers, taking appropriate care with the clamping of the shortfiber, and making an average of measurements on at least 10 fibers.Generally, at least 3 sets of measurements (each for 10 fibers) areaveraged together to provide values for the parameters determined.

Filament Denier

Denier is the linear density of a filament expressed as weight in gramsof 9000 meters of filament. Denier can be measured on a Vibroscope fromTextechno of Munich, Germany. Denier times (10/9) is equal to decitex(dtex). Denier per filament can be determined gravimetrically inaccordance with ASTM Standard Test Method D 1577.

Tenacity at Break

Tenacity at break (T) is the maximum or breaking force of a filamentexpressed as force per unit cross-sectional area. The tenacity can bemeasured on an Instron model 1130 available from Instron of Canton,Mass. and is reported as grams per denier (grams per dtex). Filamenttenacity at break (and elongation at break) can be measured according toASTM D 885.

Filament Tenacity at 7% Elongation

Filament tenacity at 7% elongation (T₇) is the force applied to afilament to achieve 7% elongation divided by filament denier. T₇ can bedetermined according to ASTM D 3822.

Yarn Strength

Strength of the spun nylon/cotton yarns herein can be quantified via aLea Product value or yarn breaking tenacity. Lea Product and skeinbreaking tenacity are conventional measures of the average strength of atextile yarn and can be determined in accordance with ASTM D 1578. LeaProduct values are reported in units of pounds force. Breaking tenacityis reported in units of cN/tex.

Fabric Weight

Fabric weight or basis weight of the woven fabrics herein can bedetermined by weighing fabric samples of known area and calculatingweight or basis weight in terms of grams/m² or oz/yd² in accordance withthe procedures of the standard test method of ASTM D 3776.

Fabric Grab Strength

Fabric grab strength can be measured in accordance with ASTM D 5034.Grab strength measurements are reported in pounds-force in both warp andfill directions.

Fabric Tear Strength—Elmendorf

Fabric tear strength can be measured in accordance with ASTM D 1424titled Standard Test Method for Tearing Strength of Fabrics byFalling-Pendulum Type (Elmendorf) Apparatus. Grab strength measurementsare reported in pounds-force in both warp and fill directions.

Fabric Abrasion Resistance—Taber

Fabric abrasion resistance can be determined as Taber abrasionresistance measured by ASTM D3884-01 titled Abrasion Resistance UsingRotary Platform Double Head Abrader. Results are reported in terms ofcycles to failure.

Fabric Abrasion Resistance—Flex

Fabric abrasion resistance can be determined as Flex abrasion resistancemeasured by ASTM D3885 titled Standard Test Method for AbrasionResistance of Textile Fabrics (Flexing and Abrasion Method). Results arereported in terms of cycles to failure.

The features and advantages of the present invention are more fullyshown by the following examples which are provided for purposes ofillustration, and are not to be construed as limiting the invention inany way.

EXAMPLES

The invention of some embodiments can be illustrated by the followingexamples. In the examples herein, various nylon staple fibers areproduced. The procedures used involve an SPP phase, an filament spinningphase, a drawing and annealing phase and a staple fiber productionphase. Staple fibers so produced are then spun with cotton staple fibersinto NYCO yarn.

In all instances, precursor nylon polymer flake is fed to a solid phasepolymerization (SPP) vessel. The precursor flake polymer is homopolymernylon 6,6 (polyhexamethylene adipamide) containing a polyamidationcatalyst (i.e., manganous hypophosphite obtained from OccidentalChemical Company with offices in Niagara Falls, N.Y.) in concentrationby weight of 16 parts per million. The precursor flake fed into the SPPvessel has a formic acid RV of about 48.

In the SPP vessel, conditioning gas is used to increase the RV of thenylon polymer flake to a value of from about 75 to 85, e.g., about 80.This higher RV flake material is removed from the SPP vessel and is fedto a twin screw melter and then to a spin pack for melt spinning througha spinneret into filaments. Filaments extruded through the spinneret arepassed through a quench zone and then converged into a continuousfilament tow.

The continuous filament tow is then drawn and annealed in a two stageoperation using the apparatus and procedures described in U.S. Pat. No.5,011,645. Various effective draw ratios are used in this two stageprocedure as shown in Table 1. The tows were drawn to a relativelysmaller denier per filament (dpf) as also shown in Table 1. The drawnand annealed tow is then cooled to below 80° C. and is cut into nylonstaple fibers having the characteristics shown in Table 1.

TABLE 1 Example Effective Tenacity Tenacity at 7% # Draw Ratio DPF (T)(T₇) 1 2.78 1.69 6.37 3.57 2 2.81 1.77 6.48 4.28 3 2.82 1.75 6.93 3.59 42.82 1.71 6.38 3.74 5 2.85 1.68 6.99 3.95 6 2.86 1.69 6.77 3.91 7 2.891.71 7.20 4.09 8 2.90 1.68 6.75 3.70 9 2.93 1.69 6.17 3.47 10 2.98 1.626.70 4.11 11 3.03 1.66 7.26 4.45

Similar nylon staple fibers are formed from the same relatively high RVnylon polymer material, using instead slightly higher spun denier supplyand corresponding higher effective draw ratios and producing staplefiber having higher denier per filament values. Characteristics of thesefibers are shown in Table 2.

TABLE 2 Example Effective Tenacity Tenacity at 7% # Draw Ratio DPF (T)(T₇) 12 3.35 2.61 6.89 3.38 13 3.45 2.61 6.12 3.43 14 3.50 2.58 7.073.58 15 3.55 2.57 6.64 3.44 16 3.60 2.56 6.94 3.63

The nylon staple fibers from Table 1 are ring spun into nylon/cottonblend yarns with various nylon to cotton staple fiber ratios. Such yarnshave very good yarn strength as determined by measuring their breakingtenacity and Lea Product values. These yarns can have a Lea productvalue ranging from 2800 to 3600 and breaking tenacity from 17.5 cN/Texto 22.5 cN/tex when used in a 50/50 nylon/cotton blend and yarn countsin the 16/1 to 20/1 range Yarns produced from ring spun blends of theTable 1 nylon staple fibers with cotton staple in a nominal 50:50 blendare woven into 2×1 twill fabric constructions. In such fabrics, 20/1cotton count yarns are woven in the warp direction and the 16/1 or 20/1cotton count yarn are woven in the fill direction depending upon weight.The fabrics made using the mentioned yarns can range in weight from 5.6to 6.5 oz/yd2. As used herein, cotton count refers to the yarn numberingsystem based on a length of 840 yards, and wherein the count of the yarnis equal to the number of 840-yard skeins required to weigh 1 pound.Fabrics prepared in this manner from such nylon staple containing yarnsexhibit very good grab and tear strength properties. These fabrics canhave a grab strength ranging from 200 lbf to 275 lbf in the warpdirection and 90 to 175 lbf in the fill direction. These fabrics canalso have Elmendorf tear strength values ranging from 12.0 lbf to 14.5lbf in the warp direction and 10.0 lbf to 12.0 lbf in the filldirection. It will be appreciated by those skilled in the art thatheavier fabrics weights, such as those greater than 6.5 oz/yd², will beexpected to exhibit even higher grab and tear strengths. (Moreimportantly, these fabrics have excellent abrasion resistant asdetermined by both Taber and Flex Abrasion testing. Flex Abrasion valuesfor the above mentioned fabrics can range from 60,000 cycles to as highas 70,000 cycles in the warp direction and 68,000 to 80,000 in the filldirection. Values are to be compared in the “as received” condition.Taber abrasion values for the above mentioned fabric constructions canrange from 600 cycles to 1900 cycles in the “as received” or unlaunderedstate.

While there have been described what are presently believed to be thepreferred embodiments of the invention, those skilled in the art willrealize that changes and modifications may be made thereto withoutdeparting from the spirit of the invention, and it is intended toinclude all such changes and modifications as fall within the true scopeof the invention.

1. A process for preparing nylon staple fibers, said process comprisingmelt-spinning nylon polymer into filaments, quenching said filaments andforming one or more tows from a multiplicity of said quenched filaments,subjecting said tow(s) to drawing and annealing, and converting saiddrawn and annealed tow(s) into staple fibers suitable for forming intospun yarn; wherein; A) the nylon polymer melt spun into filaments has aformic acid relative viscosity (RV) of from 65 to 100; B) the drawingand annealing of the tow(s) is carried out in a two-stage continuousoperation conducted at a total effective draw ratio of from 2.3 to 4.0,said operation comprising a first drawing stage wherein from 85% to97.5% of the drawing of the tow(s) occurs and a second annealing anddrawing stage wherein said tow(s) is/are subjected to an annealingtemperature of from 145° C. to 205° C.; said operation being followed bya cooling step wherein said drawn and annealed tow(s) is/are cooled to atemperature of less than 80° C.; and C) the tow(s) is/are maintainedunder a controlled tension throughout said two stage continuousoperation.
 2. A process according to claim 1 wherein said staple fibershave a denier per filament of from 1.0 to 3.0, a tenacity at break of atleast 6.0 grams per denier and a load-bearing capacity of greater than2.5, grams per denier measured as tenacity (T₇) at 7% elongation.
 3. Aprocess according to claim 1 wherein the relative viscosity (RV) of thenylon polymer ranges from 70 to
 85. 4. A process according to claim 1wherein said staple fibers have a denier per filament of from 1.55 to1.8, a tenacity at break greater than 6.5 grams per denier, and aload-bearing capacity of from 3.0 to 5.0 grams per denier measured astenacity (T₇) at 7% elongation.
 5. A process according to claim 4wherein said drawing and annealing of said multifilament tow(s) isconducted at a total effective draw ratio of from 2.5 to 3.0.
 6. Aprocess according to claim 1 wherein said staple fibers have a denierper filament of from 2.1 to 3.0, a tenacity at break of greater than 6.5grams per denier, and a load-bearing capacity of from 3.0 to 4.0 gramsper denier measured as tenacity (T₇) at 7% elongation.
 7. A processaccording to claim 6 wherein said drawing and annealing of saidmultifilament tow(s) is conducted at a total effective draw ratio offrom 3.25 to 3.75.
 8. A process according to claim 1 wherein said nylonpolymer is prepared by subjecting nylon flake material to solid phasepolymerization (conditioning) to attain the desired relative viscosity(Rv) and by then melt spinning said polymer into filaments.
 9. A processaccording to claim 1 wherein said first drawing stage is carried out ata temperature of from 80° C. to 125° C., and said second annealing anddrawing stage is carried out at a temperature of from 165° C. to 205° C.10. A process according to claim 1 wherein said nylon polymer isselected from the group consisting of polyhexamethylene adipamide (nylon6,6) and polycaproamide (nylon 6).
 11. Nylon staple fibers prepared by aprocess according to claim
 1. 12. An article comprising nylon staplefibers made from nylon having a formic acid relative viscosity (RV) offrom 65 to 100, more preferably from 70 to 85, wherein said fibers havea denier per filament of from 1.0 to 3.0, a tenacity of at least 6.0grams per denier and a load-bearing capacity of greater than 2.5, gramsper denier, measured as tenacity (T₇) at 7% elongation.
 13. The articleof claim 12 wherein said nylon staple fibers have a denier per filamentof from 1.55 to 1.75, a tenacity at break of greater than 6.5 grams perdenier, and a load-bearing capacity of from 3.0 to 5.0 grams per deniermeasured as tenacity (T₇) at 7% elongation.
 14. The article of claim 12wherein said nylon staple fibers have a denier per filament of from 2.1to 3.0, a tenacity at break of greater than 6.5 grams per denier, and aload-bearing capacity of from 3.0 to 5.0 grams per denier measured astenacity (T₇) at 7% elongation.
 15. The article of claim 12 wherein saidnylon staple fibers are made from nylon polymer material selected fromthe group consisting of polyhexamethylene adipamide (nylon 6,6) andpolycaproamide (nylon 6).
 16. The article of claim 12 wherein said nylonstaple fibers range in length from 2 to 13 centimeters (0.79 to 5.12inches).
 17. The article of claim 12 wherein said article comprises atextile yarn suitable for weaving into fabrics to improve abrasionresistance of said fabric, said yarn comprising blended cotton staplefibers and nylon staple fibers in a weight ratio of cotton staple fibersto nylon staple fibers ranging from 20:80 to 80:20.
 18. A textile yarnsuitable for weaving into fabrics to improve abrasion resistance of saidfabric, said yarn comprising blended cotton staple fibers and nylonstaple fibers in a weight ratio of cotton staple fibers to nylon staplefibers ranging from 20:80 to 80:20; wherein substantially all of saidnylon staple fibers are made from nylon having a formic acid relativeviscosity (RV) of from 65 to 100, said nylon fibers being furthercharacterized by having a denier per filament of from 1.0 to 3.0, atenacity of at least 6.0 grams per denier and a load-bearing capacity ofgreater than 2.5, grams per denier, measured as tenacity (T₇) at 7%elongation.
 19. A textile yarn according to claim 17 which exhibits aLea product value of at least 2800 or a breaking tenacity of at least 18cN/tex, based on a standard 50:50 nylon:cotton ratio.
 20. An NYCO fabricwoven from textile yarns according to claim
 17. 21. A NYCO fabric wovenfrom textile yarns in both a warp and weft (fill) direction wherein saidtextile yarns woven in at least one direction comprise blended cottonstaple fibers and nylon staple fibers in a weight ratio of cotton staplefibers to nylon staple fibers ranging from about 20:80 to 80:20; andfurther characterized in that said nylon staple fibers are made fromnylon having a formic acid relative viscosity (RV) of from 65 to 100,more preferably from 70 to 85, said nylon fibers further having a denierper filament of from 1.0 to 3.0, a tenacity of at least 6.0 grams perdenier and a load-bearing capacity of greater than 2.5, grams perdenier, measured as tenacity (T₇) at 7% elongation.
 22. A NYCO fabricaccording to claim 20 wherein the yarns woven in the fill directioncomprise nylon staple fibers having a denier per filament of from 1.6 to1.8 and the yarns woven in the warp direction comprise nylon staplefibers having a denier per filament of from 2.3 to 2.7.
 23. A NYCOfabric according to claim 20 having a fabric weight of 200 grams/m² (6.0oz/yd²) or less.
 24. A 2×1 twill NYCO fabric according to any of claims20 to 23 having a grab strength of 190 lbs or greater in the warpdirection and 80 lbs or greater in the fill direction, measured inaccordance with ASTM D
 5034. 25. A 2×1 twill NYCO fabric according toclaim 20 having a Taber Abrasion Resistance of at least 600 cycles tofailure, and more preferably at least 1200 cycles to failure, measuredin accordance with ASTM D
 3884. 26. A 2×1 twill NYCO fabric according toclaim 20 having a Flex Abrasion of at least 55,000 cycles, morepreferably 65,000 cycles to failure as measured in accordance with ASTMD 3885.